This invention relates to an electrode apparatus including means for applying a compressive load to the electrode and also to a battery and methods employing such an electrode apparatus.
The number of times that a metal electrode, for example an alkali metal anode (i.e., the negative electrode), of an electrolytic cell (battery) can be repeatedly discharged and recharged usually determines the reversibility of the battery. Assuming an excess of electrolyte, the reversibility (R) is the number of complete charges and discharges (cycles) obtainable from a cell, and is given by the product of the number of turnovers (T) achievable for the electrode times the ratio (.alpha.) of the amount of metal contained in the electrode to the stoichiometric amount of metal required for complete reaction of the opposite electrode (i.e., R=.alpha. T). A turnover (T) is defined as one complete stripping (removal) of the metal from the electrode followed by a complete amalgamation (replating) of the metal onto the electrode. In general, this process cannot be repeated indefinitely because corrosion or physical isolation of the metal within the electrode structure renders it progressively more and more difficult to strip. In some cases, the metal becomes inaccessible for stripping and becomes electrochemically inactive. To compensate for the progressive loss of active metal available for stripping, batteries often include more metal in the electrode than is required for complete reaction with the electrolytically active component of the opposite electrode. Thus, the reversibility is generally a function of the method of stripping and replating, the quantity of metal available in the electrode and the quantity of electrolyte available.
For example, with free-standing (unpressurized) lithium electrodes, a battery has a maximum of between about 1.6-2.5 turnovers, using electrolytes consisting of 1 M LiAsF.sub.6 or 1 M LiC10.sub.4 in proplyene carbonate. It would be highly desirable to be able to increase the reversibility of such electrodes and batteries.